West Nile Disease has developed as a major mosquito borne health problem in the United States. No therapy is known to be effective. Animal models suggest that immune serum may be beneficial. A national protocol has been developed in collaboration with the NIAID Viral Studies Group to study the efficacy of high titer immunoglobulin, obtained from Israel, compared to appropriate placebos. The study is randomized and double blinded. It has opened at 30 centers nationally including the Clinical Center. Six patients have been enrolled to date, including one at the Clinical Center. This protocol is a model for intramural-extramural collaboration to meet the challenge of a new, emerging infection.